Token Bucket Burst Behavior in Traffic Shaping

When using token bucket traffic shaping, the burst rate (Be + Bc) can only be achieved temporarily for one Tc interval after a period of inactivity. For example, if you have a CIR of 256 kbps and burst rate of 512 kbps:

  • The burst rate of 512 kbps occurs only once after inactivity
  • After the initial burst, the rate returns to the CIR (256 kbps)
  • The Be (Excess Burst) bucket is not refilled until another period of inactivity occurs
  • Thus, sustaining the burst rate continuously is impossible since it requires a constantly full Be bucket, which contradicts token bucket mechanics

This behavior is by design as token buckets are meant to accommodate temporary bursts while maintaining the configured CIR over time.

https://networklessons.com/quality-of-service/qos-traffic-shaping-explained

https://networklessons.com/quality-of-service/traffic-shaping-on-cisco-ios

https://networklessons.com/quality-of-service/shaping-with-burst-up-to-interface-speed

https://networklessons.com/quality-of-service/peak-traffic-shaping-on-cisco-ios